The present invention relates in general to pressure relieving valves, and in particular to a valve arrangement for a venting conduit, particularly for use in connection with pumps delivering gas- or vapor-forming liquid.
Gas or vapor bubbles in a liquid are prone to collapse suddenly when pressure of the liquid is increased, whereby powerful shockwaves in the liquid are generated resulting in overloads of machine parts conducting the liquid. Particularly the inlet and delivery valves in pumping systems are sensitive to such excessive loads and may become damaged or even destroyed.
Pumps are known which are provided with venting conduits branching from a zone of the working space of the pump in which gases or vapors are collected. To each venting conduit is assigned a special auxiliary pump which is conducted for delivery of mixtures of gases or vapors with the liquid and which feeds this mixture from the collecting zone into the pressure conduit of the pump. The disadvantage of such an auxiliary venting pump is its expensive design because the pump must be capable of delivering without interference both gas and liquids.
Instead of the auxiliary pump it has been also devised to provide the main pump with a venting conduit connecting the gas or vapor collecting zone of the main pump to its pressure conduits. The venting conduit cooperates with a backpressure or pressure relieving valve which is permanently opened in the venting direction and closed in the backpressure direction. The pressure relieving valve, however, must be capable to open at a smaller pressure difference than the delivery valve of the main pump arranged between the liquid discharge zone of the working space and the pressure conduit. This mutual adjustment of the pressure relieving valve and of the delivery valve usually necessitates to design the delivery valve with a relatively high resistance and consequently the main pump must operate with a relatively high power.